Treatment of staff is another huge factor.
For the UK at least, the majority of staff working on the ramp (with the exception of those on very old contracts) will be earning what you could earn in your average supermarket, and forced to work highly unsociable hours at the same time in all weather conditions.
Where I work, our minimum rest period between shifts is 8(!) hours. By the time you've left the office and got to the staff car park (15-20 minutes by bus or walking) and driven home, that's about 1 hour, which leaves you with 6 hours at home. Add your dinner and a shower to that and you're looking at 4 hour sleep between 12 hour shifts
Equipment is outdated and poorly maintained, with some stuff being 40+ years old